Hi Will, On Mon, Apr 22, 2013 at 05:41:12PM +0100, Will Deacon wrote: > Hi Lorenzo, > > On Mon, Apr 22, 2013 at 04:27:22PM +0100, Lorenzo Pieralisi wrote: > > Code relying on the reg property size to be 4-bytes will break when > > dtb compiled for 64-bit kernels are used to boot a 32-bit system so > > kernel code relying on that (bogus) assumption must be updated properly. > > So that code currently includes kvmtool, and I think it's unfair to break > it: > > - kvmtool can boot either 32-bit or 64-bit guests under a 64-bit > kernel and only AFF0 is exposed by the KVM host (containing the > vcpu id). This allows us to use a single cell for the reg > property, regardless of the guest payload. > > - It always sets the #address-cells property correctly, so if it > passes a 32-bit reg property, then #address-cells will be 0x1 > > - This scheme worked fine with older kernels > > Why can't we instead allow the kernel to zero extend single-cell CPU reg > properies on 64-bit systems? We can always check them against the logical > map and barf if they don't match what's sitting in the hardware, without > penalising machines which don't make use of the upper bits. Given that > people *will* run 32-bit OSs on 64-bit CPUs (a use-case which we allow), I > don't think penalising 64-bit software is the right thing to do. > > Thoughts? I notice Catalin has some patches queued for arm64 which > unconditionally use of_property_read_u64, but I have a patch to honour the > #address-cells property instead.
Basically you want me to rule out passing a dtb with cpus node having #address-cells == 2 to a 32-bit kernel, correct ? Or put it another way: - a 32-bit kernel must always get passed a dtb with cpus node #address-cells == 1. If the system is ARMv8 with CPUs having MPIDR_EL1[63:32] != 0x0, well, running 32-bit kernel on it is not the safest thing to do anyway. - a 64 bit kernel can get passed a dtb blob with configurable #address-cells [1,2]. If MPIDR_EL1[63:32] is == 0, #address-cells can be set to 1 and the OS must zero extend the reg property. #address-cells == 1 implies -> zero extension required in the OS. It makes sense. I disagree on the check you mentioned, we are not able to probe MPIDR_EL1, so if the kernel gets passed wrong reg values we have a problem, logical_map depends on DT, if DT assumes MPIDR_EL1[63:32] is 0 but it is not there is no way we can recover. I will update the bindings and arm32 parsing code if nobody objects. Lorenzo _______________________________________________ devicetree-discuss mailing list devicetree-discuss@lists.ozlabs.org https://lists.ozlabs.org/listinfo/devicetree-discuss
